F1 endonuclease?

The Genetrapper kit from Gibco/BRL uses "F1 phage endonuclease" to
generate a single-stranded nick, which is then propagated by ExoIII to
yield ss circular DNA. Does anybody know anything about this enzyme? Does
it hit one strand preferentially? Is it commercially available other than
in the kit?
Cheers,
Eric.